Lightning arrester with pressure relief means

ABSTRACT

Electrical surge protection apparatus, such as lightning arresters, in a fracturable housing are provided with a flexible diaphragm closing an opening of the housing and resting in a support means that has one or more projections extending substantially parallel with the diaphragm when it is unstressed. Pressure buildup within the housing causes the diaphragm to be distended and to rupture due to cutting by the projections. Such pressure relief means can be implemented in arresters that have provision for creation of an external arc upon failure so that within a structure that is simple and relatively easy to fabricate there can be provided both pressure venting and arc transfer means.

Unite States Patent Carothers et al.

LIGHTNING ARRESTER WITH PRESSURE RELIEF MEANS Inventors: Charles H. Carothers; Philip W. Bogner,

both of Bloomington, Ind.

Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: July 29, 1970 Appl. No.: 59,177

References Cited UNlTED STATES PATENTS Ackermann ..3 l 7/ 66 Sorrow ..317/66 X 1 Feb. 22, 1972 Primary Examiner-William M. Shoop, .lr.

Assistant Examiner'Harvey Fendelman Attorney-A. T. Stratton, F. P. Lyle and Gordon H. Telfer [5 7] ABSTRACT Electrical surge protection apparatus, such as lightning arresters, in a fracturable housing are provided with a flexible diaphragm closing an opening of the housing and resting in a support means that has one' or more projections extending substantially parallel with the diaphragm when it is unstressed. Pressure buildup within the housing causes the diaphragm to be distended and to rupture due to cutting by the projections. Such pressure relief means can be implemented in arresters that have provision for creation of an external arc upon failure so that within a structure that is simple and relatively easy to fabricate there can be provided both pressure venting and are transfer means.

6 Claims, 3 Drawing Figures PAIENTEUFEB 22 I972 2 R m B O F 3 l 7 m 3 v n z u YViTNESSES $5 n mmw WPOV m w H M m WP% h C ATTORNEY LIGHTNING ARRESTER WITH PRESSURE RELIEF MEANS BACKGROUND OF TI-IE INVENTION 1. Field of the Invention The invention relates to lightning arresters which have means for venting gases that are formed therein upon failure without encountering safety hazards and, further, to such arresters that permit transfer of the arc to an external path.

2. Description of the Prior Art 7 Failure of lightning arresters is generally attributed to entrance of moisture therein and can be substantially avoided by using reliable seals, such as solder seals, and effectively testing the apparatus before use. However, even a very occasional failure is desirably avoided because of the common location of arresters, particularly distribution lightning arresters, where an explosive failure presents a safety hazard-to persons who may be nearby. An arrester may fail in that it is unable to interrupt the flowof power follow current or otherwise it fails to establish or maintain its normal insulating characteristic as it should. Such characteristic is determined by the performance of resistive elements, such as silicon carbide valve blocks, and a spark gap assembly as are typically employed in arresters. The uninterrupted power follow current becomes equal to system fault current flowing through the arrester and results in overheating of the arrester elements and formation of arcs that cause evolution of gases from the resistive elements and electrodes therein. Under such conditions there is a rapid increase in the pressure within the arrester housing that can result in an explosion that shatters the rigid insulating housing, usually of porcelain, with substantial risk to nearby personnel and equipment.

There has in the past been employed over an opening of the housing a diaphragm that is subject to rupture upon buildup of pressure in the housing to relieve that pressure prior to reaching the level at which an explosion of the housing can occur. In some forms such apparatus includes a pointed member or sharp cutting edge directed toward the diaphragm that is brought into contact with it to rupture it when the diaphragm expands sufficiently. US. Pat. Nos. 2,915,674 and 2,928,016 are examples of such prior art.

Such apparatus that has a piercing element normally spaced from the unflexed diaphragm requires a certain time for ex pansion of the diaphragm to the piercer. That time may be longer than desirable or, at least, requires considerable control of the spacing in assembly and handling to ensure consistent results between units. On the other hand, if the diaphragm were to rest directly on a point or cutting blade directed toward it there would be substantial risk of premature damage to the diaphragm in assembly, handling or use. In use normal thermal cycling causes expansion and contraction of the air in the housing that flexes the diaphragm.

There remains an interest in providing reliable diaphragm rupturing configurations in designs that are readily implemented, particularly adaptable to low-cost distribution arresters and particularly with those that provide the additional function of transferring the arc ofa failed arrester to an external path for periods sufficient to enablecurrently available fault clearing devices to-locate and clear the fault that appears in the system due to the failed arrester.

SUMMARY OF THE INVENTION By the present invention a lightning arrester that has a flexible diaphragm closing one end thereof is provided with a support cap that includes one or more projections extending substantially parallel to and supporting the diaphragm in its normal position. The diaphragm shears when internal pressure causes expansion of the diaphragm with release of gases from the inside of the housing. This amount of pressure relief will prevent arrester porcelain rupture for currents up to about 3,000 amperes. The combination preferably includes a gas deflector which has a discharge port to direct the gases, that are highly ionized, in a direction to enable formation of an arc external to the housing. While normally required at only one end of a distribution-type arrester, if necessary or if applied to larger types of arresters, such pressure venting and gas deflection means may be provided at both ends. Preferably, the valve blocks of the arrester are located proximate the end or ends of the housing with a diaphragm to provide quickest pressure relief.

DESCRIPTION OF THE DRAWING FIG. 1 is an elevation view of a lightning arrester that may embody the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, a lightning arrester in accordance with this invention comprises a generally cylindrical housing 10 of a rigid insulating material such as porcelain held within a mounting clamp 12 for attachment with a structural support 14 (only partially illustrated). The housing contains spark gaps and resistive elements 16 (FIG. 2) in accordance with known practice that are not detailed herein but are generally represented by the element at the lowermost portion of the housing which may be the final valve block of the arrester.

In this embodiment the top of the arrester housing 10 is closed by a cap 18 having a terminal stud 20 for connection with a line or system to be protected. The topcap 18 preferably includes an arcing tab or finger 22 extending laterally therefrom whose function will be subsequently described.

At the lower end of the housing 10 there is provided closure means including a flexible diaphragm 24 extending completely across and sealing the lower opening of the housing 10. The diaphragm 24 rests within a bottom support cap 26 that is tightly secured by a solder seal 28 and possibly also a cemented or gasket joint 27 to the end of the housing 10. The functional elements 16 are supported on a support plate 30 with apertures 31 therein to permit gases to reach the flexible diaphragm. In the illustrated embodiment gasket 27 is between a lateral flangelike portion of the support plate 30 and the end of housing 10. The support plate 30 holds the internal elements 16 in place even if the diaphragm ruptures. Thus, nothing is dropped from the housing and the diaphragm 24 carries no mechanical load. The diaphragm 24 rests within the support cap 26 which is shown by itself in a top view in Figure 3. The support cap includes a generally axially extending flange member 32 and an annularly extending support portion 33 on which the diaphragm 24 directly rests. The support portion 33 includes projections 34 (here with optional corrugations 35 for extra stiffness) that extend substantially parallel to the diaphragm when it is in its normal unstressed position. The diaphragm rests directly on the substantially planar surfaces of the projections 34. The support cap 26 also has axially extending legs 36 depending downwardly from the annular portion 33 thereof. The legs 36 are attached by rivets 37, or the like, to a deflector 38 that is an essentially cuplike member with a laterally extending portion 39 providing a discharge port 40 directed axially back toward the top of the arrester, while avoiding flashover to any adjacent equipment. At the lower portion of the deflector a grounding stud 42 and/or a disconnector device 44 are provided as are conventionally used to terminate arrester assemblies.

The flexible diaphragm may conveniently be of metal, although other flexible materials such as plastic, rubber, or a thin glass may alternatively be used. Copper having a thickness of about 0.01 inch is a more specific example of a suitable diaphragm.

The support cap 26 can be advantageously formed by stamping a single blank of material, e.g., brass about one-sixteenth inch thick. It should be rigid enough to support the diaphragm and attach to the deflector without moving. The points of projections 34 are directed in a plane parallel to that of the unflexed diaphragm. The configuration shown in FIG. 3 has been successfully employed but other designs in which the projections extend closer to the center of the diaphragm could be used to provide somewhat quicker venting.

In normal operation, an electrical path is provided from stud 20 and topcap 18 through the internal arrester elements to the support plate 30, diaphragm 24, support cap 26, deflector 38 through to the disconnector 44 and grounding stud 42. In any instance in which the arrester is unable to terminate the power follow current and pressure builds up in it, the diaphragm 24 bows out and is sheared by the projections 34 of the support cap 26 so that the gases within the housing pass out through the deflector 38 in a manner that an external are 41 is created between it and the arcing tab 22 of the top cap 18, such are being sustainable for a few cycles of operation so as to permit fault location and clearing.

The support cap 26, which includes the projections 34 by which the diaphragm is sheared, may take various forms including one or a larger number of projections. In accordance with this invention the shearing projections 34 are substantially parallel with the diaphragm when the diaphragm is unstressed. The structure is not provided with a point or blade directed toward the diaphragm at which rupture is effected. The diaphragm can rest directly on the piercing elements that lie flat and provides quick venting upon a pressure buildup. As opposed to structures with a spaced piercer pointed toward the diaphragm, there is no need for care in establishing and maintaining a fixed spacing. As opposed to structures with the diaphragm resting directing on a point or blade, there is much less concern with devices in accordance with this invention about damage to the diaphragm in assembly, handling and thermal cycling in use. The disposition of the gas deflector provides additional protection for the diaphragm in that an installer cannot accidentally poke a wire or screwdriver through it. Furthermore, the required elements are of relatively simple configuration and can be economically formed and applied to otherwise generally conventional arresters, including low cost distribution arresters.

For distribution arresters having lengths ranging from about 7 to 18 inches and ratings ranging from 3 to kilovolts the arrangement of FIG. 1 with pressure relief only at one end of the housing has been successfully employed. With increasing rating and size, however, it has been found better to provide pressure relief at both ends, such as by using an arrangement as shown in FIG. 2 also at the top of housing 10 in FIG. 1, in order to provide adequate venting prior to fracture of the housing.

In normal distribution arrester practice, all of the valve blocks are located at one end inside the housing. Such practice is quite satisfactory where pressure relief means in accordance with this invention are provided at a single end and the valve blocks are provided at that end, as in FIG. 2. It has been found, however, that with pressure relief means at each end of the housing quicker venting results if the valve blocks are divided into groups of each housing and adjacent the diaphragms. This may be accounted for by the fact that most of the gases involved in the pressure buildup evolve from the valve blocks (as opposed to the spark gap assembly). Such an arrangement with pressure relief means adjacent valve blocks at both ends of the housing has successfully been used on distribution arresters of about 20 to 26 inches in length and ratings of from 18 to 21 kilovolts.

We claim:

1. Electrical surge protection apparatus comprising: a housing; closure means sealing an opening of said housingand including a flexible diaphragm; support means for said diaphragm having a cup-shaped portion within which said diaphragm rests and at least one pointed projection extending substantially parallel with said diaphragm when said diaphragm is unstressed for rupturing said diaphragm when forced outward by buildup of pressure in said housing.

2. The subject matter of claim 1 wherein: said housing is of rigid insulating material and contains within it spark gap and resistive elements; a support plate is annularly supported within said support'cup and has apertures permitting passage of gases from within said housing to reach said diaphragm; said support cup is sealed at its periphery to said housing; said support plate maintains said spark gap and resistive elements in relatively fixed position even in the event of rupture of said diaphragm.

3. The subject matter of claim 2 further comprising: a cuplike deflector member supported by said support cup and having a nonaxial outlet to vent gases flowing due to rupture of said diaphragm in a direction permitting formation of an external arc to an opposite end of said housing.

4. In a lightning arrester, the combination comprising: a housing of fracturable insulating material having a generally cylindrical configuration with an opening at each end; pressure relief closure means disposed at at least one end of said housing and comprising at each end where disposed a flexible diaphragm positioned within a support cap that includes in an integral member a generally axially extending flange portion, an annular portion against which said diaphragm is positioned, and at least one pointed projection from said annular portion extending parallel and next to said diaphragm, and a plurality of legs depending from said annular portion; a deflector secured to said legs and having a cuplike configuration with a lateral projection and a discharge port extending toward the 

1. Electrical surge protection apparatus comprising: a housing; closure means sealing an opening of said housing and including a flexible diaphragm; support means for said diaphragm having a cup-shaped portion within which said diaphragm rests and at least one pointed projection extending substantially parallel with said diaphragm when said diaphragm is unstressed for rupturing said diaphragm when forced outward by buildup of pressure in said housing.
 2. The subject matter of claim 1 wherein: said housing is of rigid insulating material and contains within it spark gap and resistive elements; a support plate is annularly supported within said support cup and has apertures permitting passage of gases from within said housing to reach said diaphragm; said support cup is sealed at its periphery to said housing; said support plate maintains said spark gap and resistive elements in relatively fixed position even in the event of rupture of said diaphragm.
 3. The subject matter of claim 2 further comprising: a cuplike deflector member supported by said support cup and having a nonaxial outlet to vent gases flowing due to rupture of said diaphragm in a direction permitting formation of an external arc to an opposite end of said housing.
 4. In a lightning arrester, the combination comprising: a housing of fracturable insulating material having a generally cylindrical configuration with an opening at each end; pressure relief closure means disposed at at least one end of said housing and comprising at each end where disposed a flexible diaphragm positioned within a support cap that includes in an integral member a generally axially extending flange portion, an annular portion against which said diaphragm is positioned, and at least one pointed projection from said annular portion extending parallel and next to said diaphragm, and a plurality of legs depending from said annular portion; a deflector secured to said legs and having a cuplike configuration with a lateral projection and a discharge port extending toward the other end of said housing.
 5. The subject matter of claim 4 wherein: a top cap closing the other of said openings has a laterally extending arcing tab for establishment of an external arc between it and said deflector.
 6. The subject matter of claim 4 wherein: said arrester includes among the functional elements in said housing a plurality of resistive blocks of which some are located proximate each housing end having said pressure relief closure means. 